Technical Field
The present disclosure relates to an integrated electronic device having a dissipative package, in particular dual side cooling package.
Description of the Related Art
As is known, in the majority of integrated electronic devices, for example in power devices that dissipate high amounts of heat, the current flow is of a vertical type, i.e., directed from the bottom face to the top face (or vice versa) of the body or die of semiconductor material integrating the integrated electronic device. Consequently, both the faces of the die are involved in dissipation of the heat generated during operation of the integrated electronic device.
To improve dissipation, dual side-cooling (DSC) packages are already available and enable extraction of the heat from both sides of the die.
Known DSC packages are manufactured using various assembly processes and generally have dissipative structures arranged on or coupled to both sides of the die. For example, on one side, generally the underside to be fixed to a support, such as a printed-circuit board (PCB), the dissipative structure may be formed by a metal frame on which the die is fixed and which forms access terminals of the package. On the opposite side, DSC packages include a plate (commonly known as clip), also of good heat-conducting material, in general a metal, such as copper.
An example of a device with DSC package is shown in FIGS. 1 to 3. In particular, FIGS. 1 to 3 show a device 1 of a surface-mount type that includes components encapsulated in a packaging mass 2. The packaging mass 2 is of insulating material, such as plastic, epoxy resin, or ceramic. The device 1 has two main faces 3A, 3B, a first face 3A which is designed to be mounted on a structure such as a printed-circuit board (PCB) (not shown) and a second face 3A, which is generally exposed towards the outside.
The packaging mass 2 incorporates a body or die 5 (FIG. 3) manufactured using semiconductor technologies and integrating an integrated component or circuit, for example a power transistor. Typically, in a way not shown, the die 5 may comprise a monolithic substrate of semiconductor material, such as silicon, covered by insulating layers surrounding conductive lines and connection structures, for example of aluminum. The die 5 is fixed, through a first adhesive layer 6, for example a so-called “solder” layer, to a frame 7 enabling electrical connection of the component or integrated circuit with an environment outside the device. The frame 7 comprises, in a known way, a bottom plate 7A, of a generally rectangular or square shape, and a plurality of terminals or pins 7B. The bottom plate 7A constitutes a substantial portion of the first face 3A, and the terminals 7B face the first face 3A as well as lateral faces 3C of the device 1, from which they may project (as shown in the embodiment) or to which they may be aligned (in a way not shown). In a known manner, a connection wire (not shown) connects one of the terminals 7B to a first contact pad (gate pad) formed on the body 1, and a metal clip (not shown) connects the other terminal 7B to another contact pad (source pad, not shown), which is also formed on the body 1.
The device 1 further comprises a heat-sink element 10, forming a so-called “clip”. In detail, the heat-sink element 10 comprises a top plate 10A and a support portion 10B. The top plate 10A is fixed to the die 5 via a second adhesive layer 11 (for example, a PbSnAg-based solder paste) and faces the second face 3B of the device 1, and the support portion 10B is bent towards the terminals 7B of the frame 7, to which it may be bonded through one or more adhesive portions 12, generally formed after the first adhesive layer 6.
The device 1 may be obtained by adhering the die 5 to the frame 7 through the first adhesive layer 6; adhering the heat-sink element 10 to the die 5 and to the terminals 7B through the second adhesive layer 11 and the adhesive portion 12; inserting the assembly thus obtained in a mold, including a bottom half-mold, a top half-mold, and possibly a spacer; and filling the mold with the packaging mass (see, for example, U.S. Pat. Pub. No. 2013/0154155 filed in the name of the present applicant).
Ideally, design and manufacture of the device 1 with DSC package are directed to optimize the overall thermal efficiency and the outline of the package (also referred to as “package outline assembly”—POA), wherein the exposed face (not fixed to the die 5) of the top plate 10A is coplanar to the second face 3B of the device and has a regular shape, as large as possible. To this end, some parameters are involved, among which the thickness of the second adhesive layer 11, i.e., the distance between the die 5 and the top plate 10A, and the inclination of the top plate 10A, i.e., its arrangement parallel to the die 5 and to the second face 3B of the device 1.
In fact, the thickness of the second adhesive layer 11 (also referred to as “bond-line thickness”—BLT) determines the coplanarity between the top die plate 10A and the second face 3B. In case of a small thickness of the second adhesive layer 11, during molding of the packaging mass 2, part of the material may cover the top plate 10A at least partially, thus reducing the area of the exposed face thereof and thus the effectiveness of dissipation of the heat-sink element 10, or in any case may cause the presence of a non-desired step. Instead, in case of excessive thickness of the second adhesive layer 11, the top plate 10A is arranged at a greater height than the nominal height, thus creating problems during the molding step, since the top plate 10A may interfere with the mold and get damaged during closing. Furthermore, also in this case, the risk of lack of planarity exists.
The inclination of the top plate 10A affects the coplanarity between it and the second face 3B. In fact, in case of non-zero inclination, a part of the top plate 10A may project with respect to the second surface 3B and/or a part of the top plate 10A may be at a lower level than the second surface 3B of the device 1. In either case, the desired coplanarity is not achieved. Further, also here, possible parts at a lower level may be coated by the packaging mass 2. Consequently, problems may arise of molding and/or effectiveness and in any case the device does not correspond to the desired specifications. For forming the device 1 with DSC package various solutions are known:                Flat: the top plate 10A is formed by a portion with rectangular area; this solution is very simple and provides a large dissipative area that responds also geometrically to the market; however, the indicated coplanarity is not provided; in fact, the second adhesive layer 11 is laid in a molten phase, very liquid, so that its thickness is not well controlled;        V-shape: this is similar to the flat solution, but the top plate 10A has a patterned, irregular, shape, less appreciated by the market and with a reduced exposed surface, and thus with less effectiveness as to heat dissipation as compared to the previous solution; the V-shape solution further shares the limitations indicated for the flat solution;        Dimple: the top plate 10A has a series of dimples forming portions projecting towards the die; in practice, the top plate is not planar, and the projections form a sort of spacers to preset the distance between the body and the top plate; this solution has the disadvantage that the dimples are filled with the packaging mass during molding so that the heat-sink element 10 does not have a full rectangular area, and thus there may be a reduction of effectiveness, besides having a shape that does not meet market requirements;        Coined: the top plate 10A is coined for presenting lowered internal lines designed to rest directly on the die 5; this solution has the disadvantage that it has no end-of-travel control, and it is very difficult to ensure planarity;        Downset: the heat-sink element 10 has a plurality of bands with non-planar structure; this solution does not ensure planarity; furthermore the heat-sink element 10 has a very irregular shape;        Double clip: initially, a first clip or plate of an irregular shape (possibly having dimples) is formed directly on the body or at a short distance therefrom, and then a plate, intended to remain exposed, is fixed via another adhesive layer; this solution employs a complicated and costly process due to the presence of two steps for fixing two distinct elements.        